1. Field of the Invention
The invention relates to integrated circuit nonvolatile memory. In particular, the invention relates to programmable resistive nonvolatile memory, such as phase change memory.
2. Description of Related Art
Nonvolatile memory stores data without requiring a continuous supply of power. Programmable resistive memory such as phase change memory is an example of nonvolatile memory. A high current reset electrical pulse melts and quenches the programmable resistive element into an amorphous state, raising the resistance of the programmable resistive element. A low current set electrical pulse crystallizes and lowers the resistance of the programmable resistive element.
Because the electrical pulse type determines the data that are stored in the programmable resistive RAM, and the size of the programmable resistive RAM cells helps to determine characteristics of the electrical pulse, it is critical to manufacture the programmable resistive RAM cells with the appropriate size.
Generally, a smaller programmable resistive RAM cell is associated with electrical pulses of lower magnitude. Accordingly, a smaller programmable resistive RAM cell is associated with decreased power consumption. A traditional solution to forming small programmable resistive RAM cells is to rely on a photolithographic mask that defines the small cell. However, such a mask is associated with accompanying problems, such as proper alignment of the mask with the already fabricated layers of the planar integrated circuit.
Therefore, it would be desirable to manufacture small programmable resistive RAM cells while relying less on aggressive photolithography masks to define the small cells.